ImClone Systems says its board of directors and outside advisers are reviewing Bristol-Myers Squibb's $4.5 billion bid to acquire the 83% of the biopharmaceutical company it doesn't already own. The board's initial view, however, is that the $60-per-share offer "substantially undervalues" the firm. ImClone's stock price jumped from about $45 per share before the offer to about $64 per share now. ImClone Chairman Carl C. Icahn, who owns 14% of the company, says . . .